Breakthrough achievement in scientists’ effort to redefine ‘kilogram’

A research team from Italy, Japan and Germany has made the ongoing international effort to redefine the kilogram by 2018 much easier by correlating two of the most precise measurements of Avogadro's number and obtaining one averaged value.

A research team from Italy, Japan and Germany has made the ongoing international effort to redefine the kilogram by 2018 much easier by correlating two of the most precise measurements of Avogadro’s number and obtaining one averaged value.

Avogadro is almost an unfathomably large quantity, greater than the number of grains of sand on earth or even the number of stars in the universe.

But the number, which represents the number of discrete particles like atoms or molecules in a mole of a substance, is a useful way to wrangle these tiny particles into more meaningful quantities.

The team from the American Institute of Physics has calculated Avogadro’s number several times in the past and each time they obtained a value for Avogadro’s number by counting the number of atoms in a one kilogram sphere of highly pure Si-28.

Earlier this year, the group had obtained a new value for Avogadro’s number with an uncertainty of less than 20 atoms per billion down from a 30-atom uncertainty in their 2011 value.

Currently, the kilogram weight standard is a platinum-iridium cylinder about the size of a golf ball, housed in the International Bureau of Weights and Measures in Sevres, France.

But in a day and age when science is a truly global endeavor, having just one physical standard against which all others must be calibrated is an impediment to progress, which is why the international metrology community is working to redefine the kilogram in terms of a constant of physics instead of a physical object.

Lead Researcher Giovanni Mana said that prior to redefining the kilogram, they needed to demonstrate that the new realisation was indistinguishable from the present one, to within the accuracy of the world’s best balances.

Ultimately, the redefinition of the kilogram will make precision measurement more readily available to a greater number of labs.

The research is published in the Journal of Physical and Chemical Reference Data.